A transformer combiner is an efficient way to build a high power radio frequency (RF) power amplifier. In order to increase output power level, a multi-way, such as a 2-way, a 4-way, an 8-way, or higher, are commonly used to stack RF voltage on a secondary inductor. A multi-way transformer combiner may be realized by a configuration of multiple sections of primary inductors and a single secondary of a continual inductor with only two output terminals. This configuration provides for the combination of the voltage from the multiple primary inductors to combine the power from these multiple sections together to deliver to the secondary.
In advance fabrication technologies, building a multi-way transformer combiner has several limitations on size and symmetrical layout arrangement. One design to provide a solution to these limits is an active distributed transformer using a transmission line inductor. This configuration uses a transmission line inductor based transformer with power amplifier (PA) devices placed at corners to maintain a symmetric structural layout. However, this requires gate orthogonal orientations in each differential PA pair, while some advanced complementary metal oxide field effect transistor (CMOS) fabrication technologies allow single gate orientation only.
Another approach uses a multi-section transformer having a figure eight type transformer combiner structural layout. This configuration helps to maintain single gate orientation, but it requires larger die area. In addition, first and last PAs in a PA row see slightly different surrounding metal structure. Another option uses a running track type transformer combiner, which includes a transmission line transformer layout with PA devices placed along with horizontal traces. This configuration also generates a non-symmetric layout between horizontal and vertical inductors.